This invention relates to an intake system for internal combustion engines and more particularly to an induction system that improves the running characteristics of the engine throughout the speed range and particularly at low and medium speeds.
It is generally well recognized that the running characteristics of an internal combustion engine are not particularly good at low and medium speeds, particularly if the engine is designed to achieve maximum output at the higher ends of the engine performance. One of the disadvantages of achieving smooth running and good performance at lower engine speeds is the difficulty in fully charging the chambers of the engine. Regardless of whether the engine is valved or ported, the intake charge does not flow continuously through the induction system during engine running. That is, when the intake valve or intake port is closed, the intake charge is temporarily stopped from flowing in the intake passage. When the intake valve or port again opens, the charge must be reaccelerated to induct it into the engine. This intermittent flow through the intake system results in poor charging efficiency at lower engine speeds. As the speed of the engine increases, there is a greater tendency to establish more uniform flow through the intake system and the aforenoted deleterious effects are not as noticeable.
The opening and closing of the communication of the induction system with the engine chamber which it serves also gives rise to pressure variations in the induction system. That is, when the intake is closed there will be a pressure build-up due to the inertia of the charge flowing through the intake passage. At certain engine speeds these pulsations in induction system pressure may be utilized to improve charging efficiency. That is, during times when there is a large pressure build-up subsequent opening of the intake valve will cause good charging as the high pressure inlet charge tends to force itself into the chamber. However, this characteristic is enjoyed only at certain speed ranges and at other speed ranges the pulsations will, in effect, reduce charging efficiency.
Recently, it has been discovered that the charging efficiency, particularly at lower engine speeds, can be improved by providing a plenum chamber which is in communication with the induction system between the throttle valve and the point of discharge at the induction system into the engine chamber. The use of such a plenum chamber permits the continued flow of intake charge even after the intake valve or intake port has been closed since a vacuum will have been exerted in the plenum chamber which permits the continued flow of intake charge. The volume and relationship of that volume to the induction system can be employed to tune and improve charging efficiency at certain speed ranges. However, even though such an arrangement significantly improves charging efficiency it is an object of this invention to provide an arrangement of this type which will still further improve charging efficiency over a wider range of engine speeds.
It is, therefore, a principal object of this invention to provide an induction system for an internal combustion engine that promotes charging efficiency over a wide range of engine speeds and loads.